EIS Investigation of Carbon Dioxide and Hydrogen Sulfide Corrosion Under Film Forming Conditions

by Parakala, Shilpha R.

Abstract (Summary)

The present study has been conducted to find the corrosion mechanisms and rates of an AISI 1018 steel in the presence of CO 2 and trace amounts of H 2 S using classical electrochemical techniques. The results obtained from experiments using electrochemical impedance spectroscopy measurements were theoretically analyzed by a semi-mechanistic model to reveal the conditions on the surface of the specimen used in the experiment. The experiments were designed to see the effect of different saturation values of iron carbonate and iron sulfide in the bulk solution on the corrosion rate of the sample. The experiments were conducted in a large scale (1000 lit) hastelloy flow loop at a fixed temperature of 60°C and total pressure of 7.9 bar. All experimental conditions were monitored regularly for the duration of the experiment. It was observed that the presence of trace amounts of H 2 S in the system decreased the corrosion rate significantly over time under the specific experimental conditions studied. This was due to the formation of an iron carbonate scale or iron sulfide scale, or both, which acted as a barrier to the diffusion of the corrosive species to the surface of the metal, thus decreasing corrosion rate.